There is a multiprocessor system called a directory-based cache coherent Non Uniform Memory Access (ccNUMA) including a plurality of pairs of a Central Processing Unit (CPU) and a memory where respective memories are shared by a plurality of CPUs. In the directory-based ccNUMA multiprocessor system, each CPU using a directory maintains a coherency between the data stored in a memory connected to the CPU and the data held in a cache memory by each CPU. The directory includes information, for example, on the locations of data in the distributed memories, and is managed and controlled by each CPU.
In the International Publication Pamphlet No. 2007/099583, a technique is disclosed in which a system controller has a copy of tags of a cache device and a next state transition of a data block is finally judged with a response packet upon completion of a snoop process.
A related technique is disclosed in, for example, International Publication Pamphlet No. WO 2007/099583.